Support __index__() in getrandbits(), randbytes() and others

Feature or enhancement

Support of the __index__() method in getrandbits() and randbytes() is inconsistent.

• Random.getrandbits() supports __index__(), but SystemRandom.getrandbits() does not.
• SystemRandom.randbytes() supports __index__(), but Random.randbytes() does not.

For consistence, both classes should support it.

sample() fails if its k argument is not integer. k should have __index__(), but it also should support comparison with integers and multiplication by list and integer. It is easy to make it more general, and only require __index__(). It will also produce more meaningful error.

binomialvariate() seems "working" with non-integer n argument, but the result is questionable. Passing non-integer value is most likely an error, and it would be better to detect it.

cc @rhettinger

Finde die Implementierungen und Tests für Random.getrandbits(), SystemRandom.getrandbits(), Random.randbytes(), SystemRandom.randbytes(), sample() und binomialvariate(). Vergleiche deren Behandlung von Argumenten, die keine Ganzzahlen sind, und überprüfe anschließend, dass unterstützte Argumente konsistent index() verwenden und ungültige Eingaben für binomialvariate() abgelehnt werden.